1. Field of the Invention
The present invention relates to a node connection structure and a node structure appropriate for redundancy, and more specifically to an optical node system and its switched connection method.
2. Description of the Related Art
Recently, a communications network using optical fiber has been developed, and put into practical use. A typical trunk path of an optical communications network is a ring network. Each unit of the ring network is provided with a signal branch device for transmitting an optical signal through the ring network to another network or a signal termination device.
FIG. 1 shows the configuration showing the concept of a ring network.
In FIG. 1, the signal division-multiplexing devices indicated by characters A through I are also referred to as nodes for connecting a ring network to one of another network and a signal termination device. For example, when an optical signal is input from another network to a node, the optical signal transmitted through the ring network is multiplexed with an optical signal input through another network, and transmitted to the ring network. Each node extracts an optical signal to be dropped from the optical signals transmitted through the ring network, and transmits it to another network or a signal termination device.
The conventional signal division-multiplexing device (node) extracts an optical signal through a predetermined specific path as a signal to be dropped from the trunk path, and transmits it to another network or a signal termination device. An optical signal transmitted from another network or a signal transmission device through a predetermined specific path is multiplexed by a signal division-multiplexing device with a signal transmitted through a trunk path, and transmitted to the trunk path. Such a signal division-multiplexing device is referred to as an ADM device (add/drop multiplexer which gathers signals from branch terminal stations, etc. or branches signals from a trunk path to transmit them to the branch terminal stations, etc.).
An ADM device is designed for redundancy to provide continuously services even when it becomes faulty. To attain this, a device referred to as an NPE (network protection equipment for redundancy of a network) is installed. The function of the NPE is incorporated into the conventional ADM device, and a protection switch is switched through a protection path for transmission of a signal.
Redundancy includes, in addition to switching a network between a primary system and a standby system, configuring a system 0 and a system 1 for a switch and an appliance such as an output sector of a switch, etc., providing redundancy for an appliance, looping back or retrieving an output signal before or after a fault of a ring network, etc.
As described above, the conventional ADM device is designed to connect a specific input path to a specific output path, but is not designed to connect all input paths to all output paths. Therefore, a protection switch has only the minimal switching function, and cannot correspond to newly extended functions of a protection switch.
The present invention aims at providing an optical node system having a simple configuration in which functions and equipment can easily be extended.
A first optical node system according to the present invention includes: a first node having a first switch for switching each of a plurality of optical input channels, outputting lights from a plurality of optical output channels, and containing optical switching ports larger in number than the optical input channels and the optical output channels; and a second node having a second switch for switching each of a plurality of optical input channels, outputting lights from a plurality of optical output channels, and containing optical switching ports larger in number than the optical input channels and the optical output channels. With the configuration, an output port of the second switch having no optical output channel is connected to an input port of the first switch, and an output port of the first switch having no optical output channel is connected to an input port of the second switch.
The second optical node system according to the present invention has a node having a switch including a plurality of input ports and a plurality of output ports with the plurality of input ports switchable to any of the plurality of output ports. The input ports of the switch include at least one port inputting a primary line and a standby line and a port inputting a signal from another node. The output ports of the switch include at least one port outputting a primary line and a standby line and a port outputting a signal to another node.
With the first optical node system according to the present invention, nodes can be easily interconnected using a switch, and the system can be easily extended as necessary in the future.
With the second optical node system according to the present invention, a node can be easily configured for redundancy using a complete group switch of the node. A complete group switch refers to a switch having a plurality of input ports and a plurality of output ports, and can switch all the plurality of input ports to all the output ports. Since a redundancy switch forms a complete group, and any input can be connected to any output, a considerably extensible switch can be configured. Especially, a costly and large redundancy configuration using the conventional ADM device can be improved into a smaller and less expensive configuration according to the present invention.